1. Technical Field
The present invention relates to a flat type vibration motor.
2. Description of the Related Art
In order to prevent people from being annoyed by the noise of portable electronic devices such as mobile phones, electronic games, or personal digital assistants, a variety of types of vibration generators are applied to the portable electronic devices. Particularly, the vibration generators are installed in the mobile phones and used as mute generators informing of the arrival of signals. In recent years, as mobile phones are becoming miniaturized and slimmed, the vibration generators installed in the mobile phones also require miniaturization and high performance.
The vibration generators use a variety of types of vibration motors as a vibration source. The vibration motors are classified into a flat type vibration motor and a cylinder type vibration motor according to the shape, and are classified into a brush type vibration motor and a brushless type vibration motor according to the existence or non-existence of a brush. Among them, the flat type vibration motor having the brush may be manufactured to be thin, so that this motor advantageously realizes the miniaturization of a mobile phone. For this reason, currently, the flat type vibration motor having the brush has been widely used.
FIG. 1 is a sectional view illustrating a conventional flat type vibration motor having a brush, and FIGS. 2 and 3 are a top perspective view and a bottom perspective view, respectively, illustrating a rotor of the flat type vibration motor having the brush of FIG. 1.
As shown in FIGS. 1 to 3, the conventional flat type vibration motor 10 having the brush includes a bracket 11 on which a lower substrate 13 is mounted. A casing 15 covers the upper portion of the bracket 11 to define an internal space. A shaft 12 is supported by the bracket 11. A magnet 14 which is a stator is mounted to an edge of an upper surface of the bracket 11. A rotor 16 is eccentrically and rotatably installed to the shaft 12.
Here, the rotor 16 includes an upper substrate 16a having on its lower surface a commutator 16b. A bearing 16c is rotatably supported by the shaft 12. A coil 16d and a weight 16e are mounted on the upper surface of the upper substrate 16a. A molding member 16f integrally couples the upper substrate 16a, the coil 16d, and the weight 16e with each other.
Further, one end of the brush 17 is connected to the lower substrate 13 through soldering, and the other end of the brush 17 is connected to the commutator 16b, thus transmitting external power to the coil 16d. 
In the brush type vibration motor 10 constructed as described above, when external power flows sequentially through the lower substrate 13, the brush 17, and the commutator 16b and is then supplied to the coil 16d, the rotor 16 is rotated by an electromagnetic force generated between the coil 16d and the magnet 14 and thus vibration is generated.
The rotor 16 of the conventional flat type vibration motor 10 constructed as described above is manufactured as follows. That is, the coil 16d and the weight 16e are bonded to the upper substrate 16a. The bonded assembly and the bearing 16c rotatably supported by the shaft 12 are insert molded using the molding member 16f, thus providing the rotor 16 in the form of one unit. In the rotor 16 manufactured in this way, the molding member 16f is formed throughout a whole area of the upper substrate 16a. 
However, when the injection molding process is performed with the coil 16d and the weight 16e bonded to the upper substrate 16a, oil may leak out from the bearing 16c, thus undesirably generating a noise. Further, the coil 16d may become severed or deformed. Furthermore, since the rotor 16 is manufactured in the form of one unit, production yield may be reduced.